The present invention relates generally to robotic machine tools, and, more specifically, to powder feed therein.
Robotic machine tools exist in various configurations for performing various manufacturing operations in the production of various machine components. A typical computer-controlled multi-axis machine is programmed to follow a predetermined path over the contours of a three dimensional workpiece. The workpiece may require precise welding at specific locations on its contour, or may require precise coating of its surface, for example.
In one exemplary configuration, a plasma torch or gun is mounted to the distal end of an articulated robotic arm having multiple degrees of movement such as translation or rotation or both. The machine may be programmed to aim the plasma gun toward the surface of the workpiece and follow a programmed path for automatically plasma spraying the workpiece with a suitable powder material.
For example, the workpiece may be a gas turbine engine stator vane having a complex 3-D contour requiring the deposition of a thermal barrier coating thereon by plasma spraying. In order to plasma spray a uniform coating over the entire surface of the workpiece, the plasma gun must follow a precise spraying path while depositing precise a layer of material.
The plasma spray coating is initially provided in powder form from a powder feeder joined to the plasma gun by a supply tube or conduit. The conduit must be long and flexible for permitting for permitting full multi-axis motion of the robotic arm without restraint or entanglement, and therefore introduces a substantial delay or lag in response time as powder feed rates are changed during operation.
Powder feeders are commercially available in various forms including integral controllers which permit setting of the desired powder feedrate therefrom. A common process control computer may be operatively joined to both the powder feeder and robotic machine for controlling operation thereof.
Since a change in powder feedrate communicated to the powder feeder introduces a time lag before the change in feedrate is effected at the end of the long supply conduit terminating at the plasma gun, the plasma spraying operation must be temporarily slowed or interrupted until a change in the feedrate has stabilized. This reduces the efficiency of the plasma spray operation and may affect the uniformity of the deposited plasma spray coating.
Accordingly, it is to provide a robotic machine having improved response time for changes in powder feedrates.
A robotic machine includes a robotic arm with a machine tool mounted thereto. A powder injector is mounted near the tool. A local powder feeder is mounted to the arm and includes a local conduit for supplying powder to the injector, and a load cell for measuring powder weight therein to control feedrate. A remote powder feeder is spaced from the arm, and includes a remote conduit joined to the local feeder for supplying powder thereto. A process computer controls the arm, and two feeders and effects staged delivery of the powder from the remote feeder to the local feeder for improving powder delivery response time.